Wireless optical communication system and wireless optical communication method

ABSTRACT

A wireless optical communication system can reduce the power consumption needed for light emission by a controlled node and suppress a modulated signal component, other than the modulated signal of input data for transmission, in the modulated signal components carried by the light output of the controlled node. The controlled node includes a transmission device for transmitting input data for transmission by an infrared ray amplitude-modulated by a modulated signal of a first frequency band and a light emission control device for suspending the light emission by the transmission device for a predetermined period based on a data amount of the input data for transmission. The light emission circuit generates a light emission control signal and the transmission device stops or starts the light emission based on the light emission control signal so that the modulated signal component in the second frequency band other than the first frequency band does not exceed a maximum allowable value.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical communication system and awireless optical communication method used in the technical field ofwireless communication using infrared and other light.

2. Description of the Related Art

In the field of wireless communication using infrared ray, theInternational Electrotechnical Commission (IEC) and, in Japan, theElectronic Industries Association of Japan (EIAJ) assign sub-carrierfrequency hands.

There are various optical communication devices for unwiredcommunication using infrared rays. For example, there are remotecontrols for remote control of television sets, video cassetterecorders, etc. using infrared rays, cordless headphones receiving audiosignals etc. by wireless communication using infrared rays from audioplayers, etc.

The sub-carrier frequency band assigned for use in infraredcommunication in a remote control is 33 kHz to 40 kHz (specifically, notless than 33 kHz and less than 40 kHz), while the sub-carrier frequencyband assigned for use in transmission of audio signals in the abovecordless headphones etc. 2 MHZ to 6 MHZ (specifically, not less than 2MHZ and less than 6 MHZ).

Here, as shown in FIG. 18, assume an infrared optical communicationsystem which comprises one control node (device) 200 and a plurality ofcontrolled nodes 260, for example, three controlled nodes 260A to 260C.Also, as shown in FIG. 19, assume that the optical communication systemperforms optical communication by the time-division multiplex system.

In FIG. 18 and FIG. 19, a control block B1 is used for transmittingcontrol information from a control node 200 to the controlled nodes.

The control block B1 is periodically transmitted. A plurality of timeslots SL (four time slots SL1 to SL4 in the example shown in FIG. 19)are provided between one control block and the next control block.

The nodes transmit data by sending transfer blocks B2 (transfer blocksB2A, B2B, and B2C in the example shown in FIG. 19) in the time slots(communication time slot) SL.

As shown in FIG. 20, part of the above control block B1 is used as anenabling signal (transmission-enablng signal) indicating information onthe assignment of the time slots and indicating approval of use of thetime slots SL. The control node 200 transmits the enabling signal to thecontrolled nodes 260.

In the example of FIG. 19 and FIG. 20, referring to the enabling signalin the control block B1, first the controlled node 260A transfers atransfer block (communication block) B2A to the control node 200. Next,the control node 200 transfers the transfer block B2B to all of thecontrolled nodes 260. Then, the controlled node 260C transfers thetransfer block B2C to the control node 200.

This optical communication system uses a wide band for attaining highspeed communication. Further, to enable use without interfering withremote controls, cordless headphones, and other systems, it uses asub-carrier frequency of not less than 6 MHZ and less than 60 MHZ (ornot less than 6 MHZ and less than 50 MHZ) shown by the hatched portionin FIG. 21.

FIG. 22 is a schematic block diagram for explaining the configuration ofthe control node 200 and the controlled nodes 260.

In FIG. 22, the control node 200 comprises a transmission device(transmitter) 210 and a reception device (receiver) 220. A controllednode 260 comprises a transmission device (transmitter) 240 and areception device (receiver) 250.

The transmission device 210 of the control node 200 comprises aquadrature modulation circuit 211 and a light emission circuit 212,while the reception device 220 comprises a light reception circuit 221and a quadrature demodulation circuit 222.

Similarly, the transmission device 240 of a controlled node 260comprises a quadrature modulation circuit 241 and a light emissioncircuit 242, while the reception device 250 comprises a light receptioncircuit 251 and a quadrature demodulation circuit 252.

The quadrature modulation circuit 211 of the control node 200 modulatesa transmission signal S201 and outputs a modulated signal (carriermodulated signal) S202 composed of a frequency component of not morethan 6 MHZ and less than 60 MHZ (or not less than 6 MHZ and less than 50MHZ). The modulated signal S202 is input to the light emission circuit212.

The light emission circuit 212 performs amplitude modulation on infraredrays based on the modulated signal S202. Namely, the light emissioncircuit 212 comprises a light emitting diode for emitting an infraredray and drives the light emitting diode based on the modulated signalS202. As a result, an infrared ray S203 which is amplitude-modulatedbased on the modulated signal S202 is output from the light emissioncircuit 212.

On the other hand, the reception device 250 of the controlled node 260receives the infrared ray S203 output from the control node 200 at thereception circuit 251. Namely, the light reception circuit 251 comprisesa photodiode which receives the infrared ray S203 and converts it to anelectric signal. Also, the reception circuit 251 has, for example, ahigh-pass filter which cuts a low frequency component such as the directcurrent component of the electric signal. An output signal S204 of thereception circuit 251 is input to the quadrature demodulation circuit252.

The quadrature demodulation circuit 252 performs quadrature demodulationon the signal S204 to reproduce a reception signal S205 the same as thetransmission signal S201.

Note that the transmission device 240 of the controlled node 260 has thesame configuration as the transmission device 210 of the control node200, and the reception device 220 of the control node 200 has the sameconfiguration as the reception device 250 of the controlled node 260.

Namely, the quadrature modulation circuit 241 of the controlled node 260modulates a transmission signal S211 and outputs a modulated signal S212composed of a frequency component of not less than 6 MHZ and less than60 MHZ (or not less than 6 MHZ and less than 50 MHZ). The light emissioncircuit 242 performs amplitude modulation on an infrared ray based onthe modulated signal S212. As a result, an infrared ray S213amplitude-modulated based on the modulated signal S212 is output fromthe light emission circuit 242.

On the other hand, the reception device 220 of the control node 200receives the infrared ray from the controlled node 260 at the lightreception circuit 221, converts it into an electric signal, and cuts thedirect current component of the electric signal. It performs quadraturemodulation on the output signal S214 of the reception circuit 221 toreproduce a reception signal S215 the same as the transmission signalS211.

The emission intensity (amplitude) of the infrared ray S203amplitude-modulated based on the modulated signal S202 is shown as anexample in FIG. 23. In FIG. 23, a control block B1 and a transfer blockB2B transmitted by the control node 200 are shown.

The transfer block B2B is transferred in a time slot SL2.

Summarizing the disadvantages of the above system, when performing highspeed wireless communication using an infrared ray as explained above,there are the following disadvantages in the transmission device foremitting the infrared ray:

Since the light emission circuit of the above transmission deviceproduces an amplitude-modulated infrared ray as explained above, asshown in FIG. 23, it constantly emits an infrared ray of a certain level(having a signal strength) even when there is no transmission signal.Namely, even a node which for example transmits once in 1000 cyclesconstantly emits an infrared ray. Therefore, it emits a wasted infraredray in the remaining 999 cycles. As a result, the power consumption ofthe transmission device becomes large.

By modifying the output level of the infrared ray shown in FIG. 23 to beas shown in FIG. 24 and by making the transmission device emit theinfrared ray only when there is a transmission signal (when performingactual transmission), the power consumption can be suppressed.

However, in the power-saving method shown in FIG. 24, if the periods ofthe time slots are made shorter for higher speed communication, themodulated signal component of a sub-carrier frequency band of forexample not less than 33 kHz and less than 6 MHZ is increased in themodulated signal components carried by the modulated wave, that Is, theinfrared ray, a serious spurious wave is generated.

As a result, the components in the frequency band of the infrared raysemitted from remote controls and other existing infrared communicationdevices undesirably increase in the frequency components of the infraredray emitted from the transmission device.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a wireless opticalcommunication system for performing optical communication between aplurality of nodes using light amplitude-modulated by a modulated signalof a first frequency band which can reduce the power consumption forlight emission in the nodes and suppress modulated signal componentsother than the first frequency band among modulated signal componentscarried by the light, and a wireless optical communication method forthe same.

According to a first aspect of the present invention, there is provideda first wireless optical communication system comprising a plurality ofnodes including a first and second nodes and performing opticalcommunication at least between the first node and the second node,wherein the second node comprises a transmission means for transmittinginput data for transmission to be input to the second node to the firstnode by using light amplitude-modulated by a modulated signal of a firstfrequency band and a light emission control means for suspending lightemission by the transmission means for a predetermined period based on adata amount of the input data for transmission to be input to the secondnode so that a modulated signal component in the second frequency bandother than the first frequency band does not exceed a maximum allowablevalue.

According to a second aspect of the present invention, there is provideda first wireless optical communication method for performing opticalcommunication at least between a first node and a second node among aplurality of nodes, including the steps of transferring input data fortransmission to be input to the second node from the second node to thefirst node by using light amplitude-modulated by a modulated signal of afirst frequency band; detecting a data amount of the input data fortransmission to be input to the second node; and suspending lightemission by the second node for a predetermined period based on thedetected data amount so that a modulated signal component in a secondfrequency band other than the first frequency band does not exceed amaximum allowable value.

According to a third aspect of the present invention, there is provideda second wireless optical communication system comprising a plurality ofnodes including a first and second nodes and performing opticalcommunication at least between the first node and second node, whereinthe first node comprises a first reception means for receiving lightfrom the second node and extracting from the light data from the secondnode; an instruction information generation means for generatinginstruction information to stop light emission by the second node for apredetermined period based on amount information In the data extractedin the first reception means; and a first transmission means fortransmitting the instruction information to the second node by usinglight amplitude-modulated by a modulated signal of a first frequencyband; and the second node comprises a reception means for receivinglight from the first node and extracting from the light the instructioninformation; an amount information generation means for generatingamount information of input data for transmission to be input to thesecond node; a second transmission means for transmitting the amountinformation generated by the amount information generation means to thefirst node by using light amplitude-modulated by a modulated signal ofthe first frequency band; and a light emission control means forsuspending light emission by the second transmission means based on theinstruction information extracted by the second reception means so thata modulated signal component in a second frequency band other than thefirst frequency band does not exceed a maximum allowable value.

According to a fourth aspect of the present invention, there is provideda third wireless optical communication system comprising a plurality ofnodes including a first and second nodes and performing opticalcommunication at least between the first node and second node, whereinthe first node comprises a first transmission means for transmitting tothe second node first input data for transmission to be input to thefirst node by using light amplitude-modulated by a modulated signal of afirst frequency band; a first reception means for receiving light fromthe second node and extracting from the light data from the second node;and a light emission control means for suspending light emission by thefirst transmission means based on amount information in the dataextracted in the first reception means and data amount of the firstinput data for transmission to be input to the first node so that amodulated signal component in a second frequency band other than thefirst frequency band does not exceed a maximum allowable value; and thesecond node comprises an amount information generation means forgenerating amount information of second input data for transmission tobe input to the second node and a second transmission means fortransmitting the amount information generated by the amount informationgeneration means to the first node by using light amplitude-modulated bya modulated signal of the first frequency band.

According to a fifth aspect of the present invention, there is provideda second wireless optical communication method for performing opticalcommunication at least between a first node and a second node among aplurality of nodes, including the steps of transferring first input datafor transmission to be input to the first node from the first node to atleast the second node by using light amplitude-modulated by a modulatedsignal of a first frequency band; generating amount information ofsecond input data for transmission to be input to the second node in thesecond node; transferring the amount information from the second node tothe first node by using light amplitude-modulated by a modulated signalof the first frequency band; and suspending light emission by the firstnode for a predetermined period based on the amount informationtransferred from the second node and a data amount of the first inputdata for transmission to be input to the first node so that a modulatedsignal component in a second frequency band other than the firstfrequency band does not exceed a maximum allowable value.

In the first optical communication system according to the presentinvention, the light emission control means of the second node suspendslight emission of the transmission means of the second node for apredetermined period based on the data amount of input data fortransmission to be input to the second node.

The transmission means of the second node suspends light emission for apredetermined period by stopping and starting light emission so thatmodulated signal component in the second frequency band becomes under amaximum allowable value.

As a result, the light emission of the transmission means can besuspended for a predetermined period in accordance with the data amountof the input data for transmission, and the power consumption for thelight emission by the transmission means can be reduced.

Further, the modulated signal component of the second frequency bandgenerated by the stopping and starting of light emission in themodulated signal components carried by the modulated wave, that is, thelight, can be kept under a maximum allowable value.

In the second optical communication system according to the presentinvention, the instruction information generation means of the firstnode generates instruction information for suspending the light emissionby the second transmission means of the second node for a predeterminedperiod based on the data amount of input data for transmission to beinput to the second node.

The light emission control means of the second node suspends the lightemission by the second transmission means for a predetermined period oftime based on the instruction information transmitted from the firstnode.

The second transmission means suspends the light emission for apredetermined period by stopping and starting light emission so thatmodulated signal component in the second frequency band becomes under amaximum allowable value.

As a result, the light emission by the second transmission means can besuspended for a predetermined period in accordance with the data amountof the input data for transmission, and the power consumption for lightemission by the transmission means can be reduced.

Further, the modulated signal component of the second frequency bandgenerated by the stopping and starting of light emission in themodulated signal components carried by the modulated wave, that is, thelight, can be kept under a maximum allowable value.

In the third optical communication system according to the presentinvention, the light emission control means of the first node suspendsthe light emission by the first transmission means of the first node fora predetermined period based on the data amount of the input data forthe first transmission to be input to the first node and the data amountof the input data for the second transmission to be input to the secondnode.

The first transmission means suspends the light emission for apredetermined period by stopping and starting the light emission so thatthe modulated signal component in the second frequency band becomesunder a maximum allowable value.

As a result, the light emission by the first transmission means can besuspended for a predetermined period in accordance with the data amountsof the input data for the first and second transmission, and the powerconsumption for the light emission by the transmission means can bereduced.

Further, the modulated signal component of the second frequency bandgenerated by the stopping and starting of light emission in themodulated signal components carried by the modulated wave, that is, thelight, can be kept under a maximum allowable value.

In the first optical communication method according to the presentinvention, the second node suspends the light emission for apredetermined period based on the data amount of the input data fortransmission to be input to the second node so that the modulated signalcomponent in the second frequency band becomes under a maximum allowablevalue.

As explained above, the light emission by the second node can besuspended for a predetermined period in accordance with the data amountof the input data for transmission, and the power consumption for thelight emission by the second node can be reduced.

Further, the modulated signal component of the second frequency bandgenerated by the stopping and starting of light emission in themodulated signal components carried by the modulated wave, that is, thelight, can be kept under a maximum allowable value.

In the second optical communication method according to the presentinvention, the first node suspends the light emission for apredetermined period based on the data amount information of the inputdata for second transmission to be input to the second node and the dataamount of input data for first transmission to be input to the firstnode so that the modulated signal component of the second frequency bandbecomes under a maximum allowable value.

As explained above, the light emission by the first node can besuspended for a predetermined period in accordance with the data amountsof the input data for the first and second transmission, and the powerconsumption for the light emission by the first node can be reduced.

Further, the modulated signal component of the second frequency bandgenerated by the stopping and starting of light emission in themodulated signal components carried by the modulated wave, that is, thelight, can be kept under a maximum allowable value.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome clearer from the following description of the preferredembodiments with reference to the accompanying drawings, in which:

FIG. 1 is a schematic block diagram of the configuration of a controlnode and a controlled node included in a wireless optical communicationsystem according to a first embodiment of the present invention;

FIG. 2 is a schematic flow chart of the operation of a controlled nodeand a control operation of an MPU;

FIG. 3 is a schematic flow chart of the operation of the controlled nodeand the control operation of the MPU continued from FIG. 2;

FIG. 4 is a schematic flow chart of the operation of a control node andthe control operation of an MPU;

FIGS. 5A to 5C are views of the relationship of stopping emission of aninfrared ray by an enabling signal and time slots;

FIGS. 6A to 6C are views of the relationship of starting emission of aninfrared ray by an enabling signal and time slots continued from FIG. 5;

FIG. 7 is a view of an amplitude of an infrared ray output by acontrolled node when gradually reducing emission of the infrared ray;

FIG. 8 is a view of an amplitude of an infrared ray output by acontrolled node when abruptly increasing emission of the infrared ray;

FIG. 9 is a schematic block diagram of the configuration of a controlnode and a controlled node included in a wireless optical communicationsystem according to a second embodiment of the present invention;

FIG. 10 is a schematic flow chart of the operation of a controlled nodeand the control operation of an MPU;

FIG. 11 is a schematic flow chart of the operation of a controlled nodeand the control operation of an MPU continued from FIG. 10;

FIG. 12 is a schematic flow chart of the operation of a control node andthe control operation of an MPU;

FIG. 13 is a schematic flow chart of the operation of a control node andthe control operation of an MPU continued from FIG. 12;

FIG. 14 is a schematic block diagram of a control node and a controllednode included in a wireless optical communication system according to athird embodiment of the present invention;

FIG. 15 is a schematic flow chart of the operation of a controlled nodeand the control operation of an MPU;

FIG. 16 is a schematic flow chart of the operation of a control node andthe control operation of an MPU;

FIG. 17 is a schematic flow chart of the operation of a control node andthe control operation of an MPU continued from FIG. 16;

FIG. 18 is a view of an example of the configuration of a wirelessoptical communication system using a control node and a plurality ofcontrolled nodes;

FIG. 19 is a view of the time assignment in a wireless opticalcommunication system;

FIG. 20 is a view of an enabling signal of a time slot existing in acontrol block;

FIG. 21 is a view of a transmission frequency band of a wireless opticalcommunication system;

FIG. 22 is a schematic block diagram of the configuration of a controlnode and a controlled node included in a wireless optical communicationsystem of the related art:

FIG. 23 is a view of an example of a signal strength of an infrared rayoutput from a control node of the related art; and

FIG. 24 is a view of an example of a signal strength of an infrared rayoutput from a control node.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Below, preferred embodiments will be described with reference to theaccompanying drawings.

As embodiments of application of a wireless optical communication methodand a wireless optical communication system according to the presentinvention, assume, for example, a high speed infrared opticalcommunication system which comprises one control node and a plurality ofcontrolled nodes as shown in FIG. 18.

Also, in the wireless optical communication system according to theembodiments of the present invention, assume that optical communicationof a time-division multiplex system as shown in FIG. 19 is performed.Thus, in the embodiments of the present invention, as shown in FIG. 20,part of the control block is used as an enabling signal (transmissionenabling signal) indicating information of assignment of time slots andapproval for using the time slots.

Further, in the optical communication system according to theembodiments of the present invention, assume that a broad frequency bandis used for realizing high speed communication and that opticalcommunication is performed by using a sub-carrier frequency of not lessthan 6 MHZ and less than 60 MHZ (or not more than 6 MHZ and less than 50MHZ) as shown in FIG. 21 in order to avoid interference with remotecontrols, cordless headphones, and other infrared communication devices.

First Embodiment

FIG. 1 is a schematic block diagram of the configuration of a controlnode (a first node) 90 and a controlled node (a second node) 100 used ina wireless optical communication system of a first embodiment of thepresent invention.

Note that in FIG. 1, for simplification, the number of the control node90 is made one and the number of the controlled nodes is also made one,thereby giving an example of one-to-one optical communication, however,the invention can be applied to one-to-many optical communication aswell.

The control node 90 comprises a transmission device (transmitter) 10, areception device (receiver) 20, a microprocessing unit (MPU) 30, aswitch 31, and a signal conversion circuit 32.

The transmission device 10 and the switch 31 comprise a transmissionmeans, while the reception device 20 and the signal conversion circuit32 comprise a reception means.

The transmission device 10 comprises a quadrature modulation circuit 11and a light emission circuit 12. The light emission circuit 12 is madeto constantly emit an infrared ray. The light emission circuit 12 has alight emitting diode to emit the infrared ray.

The reception device 20 comprises a light reception circuit 21 and aquadrature demodulation circuit 22. The light reception circuit 21comprises a photodiode and a high-pass filter (HPF). The high-passfilter cuts a low frequency component such as the direct currentcomponent of an electric signal output from the photodiode and passes ahigh frequency component.

The MPU 30 is a controller in overall control of the control node 90 andhas an assignment means 30A.

The assignment means 30A assigns time slots, generates assignmentinformation, and outputs a signal (enabling signal) S7 indicating theassignment information to the signal conversion circuit 32.

The controlled node 100 comprises a transmission device (transmitter)40, a reception device (receiver) 50, an MPU 60, a switch 61, and asignal conversion circuit 62.

The transmission device 40 and the switch 61 comprise a transmissionmeans, while the reception device 50 and the signal conversion circuit62 comprise a reception means.

The transmission device 40 comprises a light emission circuit 42 and aquadrature modulation circuit 41. The light emission circuit 42 is madeto emit light based on a light emission control signal S16 input to alight emission control terminal 42T. The light emission circuit 42 has alight emitting diode for emitting an infrared ray.

Note that the light emission circuit 42 has the same configuration asthat of the light emission circuit 12. The not illustrated lightemission control terminal of the light emission circuit 12 is designedto be supplied with a light emission control signal to make the lightemission circuit 12 constantly emit light.

The reception device 50 comprises a light reception circuit 51 and aquadrature demodulation circuit 52. The light reception circuit 51comprises a photodiode and a high-pass filter (HPF). The high-passfilter cuts the direct current component of an electric signal outputfrom the photodiode.

The MPU 60 is a controller for overall control of the controlled node100 and comprises a light emission control means 60A and an amountinformation generation means 60B.

The light emission control means 60A generates a light emission controlsignal S16 and outputs it to the light emission circuit 42.

The amount information generation means 60B monitors input data fortransmission (input data) S25, generates amount information of the inputdata S25, and supplies the amount information to the light emissioncontrol means 60A.

Data is transferred from the control node 90 to the controlled node 100by the following processing.

The input data for transmission (input data) S21 is supplied to aterminal 91 of the control node 90. The input data S21 is then input tothe signal conversion circuit 32.

The signal conversion circuit 32 converts the input data S21 to a signalS6 of a format for infrared communication. The signal S6 is supplied tothe quadrature modulation circuit 11 as a transmission signal S1 via theswitch 31.

The quadrature modulation circuit 11 modulates the transmission signalS1 to generate a modulated signal (carrier modulated signal) S2comprised by a frequency component of not less than 6 MHZ and less than60 MHZ.

The carrier modulated signal S2 is input to the light emission circuit12. The light emission circuit 12 outputs an infrared ray S3amplitude-modulated based on the carrier modulated signal S2.

In the reception device 50 of the controlled node 100, the infrared rayS3 is received by the light reception circuit 51.

The light reception circuit 51 converts the infrared ray S3 into anelectric signal and generates a signal S4 in which the direct currentcomponent is cut.

The signal S4 is input to the quadrature demodulation circuit 52. Thequadrature demodulation circuit 52 performs quadrature demodulation onthe signal S4 to reproduce a reception signal S5 the same as thetransmission signal S1.

The reception signal S5 is input to the signal conversion circuit 62.The signal conversion circuit 62 performs the reverse signal processingas the signal processing for converting the input data S21 to the signalS6 in the signal conversion circuit 32 so as to invert it and generatesoutput data S23 which it outputs to the MPU 60 and the terminal 103. Theoutput data S23 includes the input data S21 or the signal S7.

On the other hand, data is transferred from the controlled node 100 tothe control node 90 by similar processing.

Input data S25 is supplied to a terminal 105 of the controlled node 100.The input data S25 is input to the signal conversion circuit 62 and theMPU 60.

The signal conversion circuit 62 converts the input data S25 into asignal S28 of a format for infrared communication. The signal S28 isinput to the quadrature modulation circuit 41 as a transmission signalS11 via the switch 61.

The quadrature modulation circuit 41 modulates the transmission signalS11 and generates a modulated signal (carrier modulated signal) S12comprised by a frequency component of not more than 6 MHZ and less than60 MHZ.

The carrier modulated signal S12 is input to the light emission circuit42. The light emission circuit 42 outputs an infrared ray S13amplitude-demodulated based on the carrier modulated signal S12.

In the reception device 20 of the control node 90, the infrared ray S13is received by the light reception circuit 21.

The light reception circuit 21 converts the infrared ray S13 into anelectric signal and generates a signal S14 where the direct currentcomponent is cut.

The signal S14 is input to the quadrature demodulation circuit 22. Thequadrature demodulation circuit 22 performs quadrature demodulation onthe signal S14 to reproduce a reception signal S15 the same as the abovetransmission signal S11.

The reception signal S15 is input to the signal conversion circuit 32.The signal conversion circuit 32 performs the reverse signal processingas the signal processing for converting the input data S25 to the signalS28 in the signal conversion circuit 62 so as to invert it and generatesoutput data S20 which it outputs to the MPU 30 and the terminal 93. Theoutput data S20 includes the input data S25 or the signal S26.

The assignment means 30A included in the MPU 30 of the control node 90assigns time slots after N cycles (N≧1) to generate a signal S7indicating assignment information based on an instruction signal S22input from the outside, such as an upper layer, to the terminal 92 orthe output data S20.

Note that while it was explained that the assignment means 30A assignsslots based on the instruction signal S22, the assignment means 30A maybe provided with a counter, a memory device, etc. and use these so thatthe assignment means 30A autonomously assigns slots and generates thesignal S7.

The signal S7 is converted into a signal S9 of a format for infraredcommunication in the signal conversion circuit 32. The signal S9 issupplied to a switchable terminal a of the switch 31.

The switch 31 receives a transfer block or a control block from thesignal conversion circuit 32 as a signal S6 at another switchableterminal b and controls the switching of the switchable terminals a andb based on a switch control signal S8 from the MPU 30.

When transmitting an ordinary transfer block, the MPU 30 controls theswitch 31 to switch to the switchable terminal b side by the switchcontrol signal S8 so that the signal S6 of the transfer block istransferred as it is as a signal S1 to the transmission device 10.

When transmitting a control block, the MPU 30 controls the switch 31 toswitch the switchable terminals a and b by a switch control signal S8 sothat the signal S9 is inserted into part of the control block. Here, theswitch 31 operates as a multiplexer. As a result, a transmission signalS1 having the configuration shown in FIG. 20 where the signal S9 isinserted in part of the signal S6 of the control block is generated

At this time, the signal S9 inserted in the control block is a signalindicating assignment information of time slots after N cycles andapproval of use of the time slots.

On the other hand, the light emission control means 60A in the MPU 60 ofthe controlled node 100 is supplied with output data S23 from the signalconversion circuit 62 and detects the control block.

The amount information generation means 60B in the MPU 60 generatesinformation of a data amount (amount information) of input data S25 andsupplies it to the light emission control means 60A.

The light emission control means 60A refers to the signal S7 in thecontrol block and decides the stopping of the emission of an infraredray, emission restarting time S, etc. based on the amount informationfrom the amount information generation means 60B.

Then, the light emission control means 60A controls the light emissionof the light emission circuit 42 by a light emission control signal S16to make stop and start emission of the infrared ray. Further, lightemission suspension information including information indicatingemission stopping and information indicating an emission restarting timeS is output as a signal S26 to the signal conversion circuit 62. Notethat the light emission suspension information may be informationindicating timings of stopping and starting the light emission,patterns, or transient characteristics.

The signal conversion circuit 62 converts the signal S26 into a signalS27 of a format for infrared communication and supplies the same to oneswitchable terminal a of the switch 61.

The switch 61 is supplied with a transfer block from the signalconversion circuit 62 as a signal S28 at the other switchable terminal band controls the switching of the switchable terminals a and b by theswitch control signal S29 from the MPU 60.

The MPU 60 switches the switch 61 by the switch control signal S29 toinsert the signal S27 to part of the signal S28 of the transfer block.The transmission signal S11 of the transfer block is output from theswitch 61 to the transmission device 40.

Operation of Controlled Node 100

Next, the operation of the controlled node 100 will be explained withreference to FIG. 2 and FIG. 3.

FIGS. 2 and 3 are schematic flow charts of the operation of thecontrolled node 100 and the control operation of the MPU 60. Here, thecontrol operation relating to the stopping and starting of the emissionof the infrared ray is shown.

First, at step F1, it is judged whether the data amount of the inputdata S25 is very small. The “very small” means a state where data to betransmitted is small and an almost empty block is transmitted whentransmitting a transfer block by using an assigned time slot. Forexample, it is judged by comparing a preset data amount with the abovedata amount.

When the data amount of the input data S25 is judged not small, the MPUwaits until the data amount of the input data S25 becomes small. Here,when an assigned time slots arrives, a transfer block including theinput data S25 is transmitted to the control node 90 in the assignedtime slot.

When the data amount of the input data S25 is small, the routineproceeds to step F2.

At step F2, it is judged whether a sufficient time has passed after thelight emission circuit 42 started to emit. The “sufficient times” meansa time of a length not causing any serious spurious waves due to anincrease of a modulated signal component in a sub-carrier frequency bandof not less than 33 kHz and less that 6 MHZ when the light emission isstopped. For example, this is judged by storing the previous emissionrestarting time in an internal memory device and determining whether apredetermined time has passed from the previous light emissionrestarting time.

When a sufficient time has not passed, the routine returns to step F1.

When a sufficient time has passed, the routine proceeds to step F3.

By judging whether a sufficient time has passed as explained above, themodulated signal component in the sub-carrier frequency band or itssquare (or power level) is made a value lower than the frequencycomponent of a reference wave or its square (or power level) by not morethan the maximum allowable value and thus a serious spurious wave is notgenerated. As an example, the power level of the sub-carrier frequencyband may be made a value lower than the power level of the referencewave by not more than 40 dB.

At step F3, it is judged whether a time slot is assigned to thecontrolled node 100 based on the enabling signal in the control blockfrom the control node 90. When the assigned time slot arrives, theroutine proceeds to step F4.

At step F4, light emission suspension information including informationindicating stopping of the infrared ray emission and informationindicating a light emission restarting time S is generated, and atransfer block including the light emission suspension information istransferred to the control node 90 by using the assigned time slot.

Specifically, by outputting a signal S26 indicating the light emissioninformation to the signal conversion circuit 62, converting it into asignal S27, and controlling the switch 61 to switch by the switchcontrol signal S29, the signal S27 is inserted in part of the transferblock and the transmission signal S11 is generated and output to thetransmission device 40.

As the light emission restarting time S, a time after the elapse of atime of an extent not generating any serious spurious waves in asub-carrier frequency band of not less than 33 kHz and less than 6 MHZis chosen.

At step F5, it is again judged whether a time slot is assigned to thecontrolled node 100. When the assigned time slot arrives, the routineproceeds to step F6.

At step F6, a light emission control signal (light emission stoppingsignal) S16 for stopping light emission is output to instruct the lightemission circuit 42 to stop light emission, then the routine proceeds tostep F7. The light emission circuit 42 stops emitting light in theassigned time slot based on the light emission control signal S16.

At step F7, it is judged whether the current time is a time T. When thetime T arrives, the routine proceeds to step F8. Here, the time T is atime a little earlier than the light emission restarting time S.

At step F8, it is again judged whether a time slot is assigned to thecontrolled node. When the assigned time slot arrives, the routineproceeds to step F9.

At step F9, a light emission control signal (light emission startingsignal) S16 for starting the light emission is output to the lightemission circuit 42 to instruct it to start emitting the light, then theroutine returns to step F1. The light emission circuit 42 startsemitting light in the assigned time slot based on the light emissionstarting signal S16.

Operation of Control Node 90

The operation of the control node 90 will be explained next withreference to FIG. 4.

FIG. 4 is a schematic flow chart of the operation of the control node 90and control operation of the MPU 30. Here, the control operationrelating to assignment of a time slot is shown. Also, a case of awireless optical communication system comprising a control node 90 andthree controlled nodes 100A to 100C will be explained.

At step G1, first, time slots are normally assigned, a control blockincluding an enabling signal corresponding to the assignment istransmitted to the controlled nodes 100A to 100C, then the routineproceeds to step G2. For example, the control node 90 performs thenormal assignment by equally assigning time slots to the control node 90and the controlled nodes 100A to 100C.

At step G2, it is judged whether light emission suspension informationincluding information of stopping an infrared ray emission andinformation of a light emission restarting time S is received byreferring to output data S20 of the signal conversion circuit 32.

When the light emission suspension information is not received, theroutine returns to step G1.

When the light emission suspension information is received, the routineproceeds to step G3.

In the following steps G3 to G6, time slots are assigned at least onceto the controlled node (for example, the controlled node 100A) whichtransmitted the light emission suspension information, and a controlblock including an enabling signal corresponding to the assignment istransmitted to the controlled nodes 100A to 100C.

This is because the time slot assigned to the node 100A is used when thecontrolled node 100A which transmitted the light emission suspensioninformation stops the emission of the infrared ray.

At step G3, a variable x is cleared and reset to 0.

At step G4, time slots are normally-assigned to the controlled nodes100A to 100C, and a control block including an enabling signalcorresponding to the assignment is transmitted to the controlled nodes100A to 100C.

At step G5, when a time slot is assigned to the controlled node 100A atstep G4, the value of the variable x is incremented to add exactly one,while when a time slot is not assigned to the controlled node 100A atstep G4, the value of the variable x is left as it is.

At step G6, whether the value of the variable x is a predetermined valueM or more (M≧1) is judged.

When the value of the variable x is less than the predetermined value M,the routine returns to step G4, where the time slots are normallyassigned.

When the value of the variable x is the predetermined value M or more,the routine proceeds to step G7.

At step G7, time slots are assigned to the controlled nodes 100B and100C other than the controlled node 100A or the control node 90, acontrol block including an enabling signal corresponding to theassignment is transmitted to the controlled nodes 100A to 100C, and theroutine proceeds to step G8.

At step G8, it is judged whether the current time is the light emissionrestarting time S.

When it is not yet the light emission restarting time S, the routinereturns to step G7, where time slots are assigned to the nodes otherthan the controlled node.

When it is the light emission restarting time S, the routine returns tostep G1.

Note that while it was explained that the normal assignment of timeslots was performed M times at steps G3 to G6, a plurality of time slotsmay be assigned to the controlled node 100A.

At step G7, time slots not assigned to the controlled node 100A areassigned to the nodes participating in the optical communication (thecontrol node 90 in FIG. 5). However, by assigning them to nodes notparticipating in the optical communication, the number of controllednodes for performing optical communication can be increased and theamount of communication of nodes other than the control node 90 and thecontrolled node 100A can be increased.

The control node 90 is made to transmit a transfer block including inputdata S21 to the controlled nodes 100A to 100C in the assigned time slotwhen that assigned time slot arrives at the control node 90.

Assigned Time Slot and Infrared Ray Emission Intensity

Next, the relationship of the emission intensity (signal strength) of aninfrared ray emitted by the light emission circuit of the transmissiondevice and the assigned time slots in a wireless optical communicationsystem according to the present invention will be explained withreference to FIGS. 5 and 6. The case of the above first embodiment willbe explained here.

FIGS. 5A to 5C are views of the relationship of stopping of infrared rayemission and time slots.

FIGS. 6A to 6C are views of the relationship of starting of infrared rayemission and time slots.

FIG. 6A is a continuation from FIG. 5C.

In the figures, “controlled n” indicates a controlled node and “controln” indicates a control node.

In FIG. 5A and FIG. 6A, assignment information of time slots included ina control block is illustrated as enabling signals K1 to K5 and K10 toK14 corresponding to the control blocks CB1 to CB5 and CB10 to CB14.

In FIG. 5B and FIG. 6B, the signal strength (amplitude) of the infraredray output by the control node 90 is shown. A control block CB and atransfer blot TB are illustrated in accordance with the amplitude.

In FIG. 5C and FIG. 6C, the signal strength (amplitude) of the infraredray output by the controlled node 100 is shown. A transfer blot TB isillustrated in accordance with the amplitude.

Note that one cycle between the control blocks CB is considered to be125 μs (microsecond) as an example in the present embodiment.

The control node 90 cyclically transmits the control blocks CB1 to CB14to the controlled node 100. The control blocks CB1 to CB14 correspond tothe enabling signals K1 to K14 of time slots. The control blocks CB1 toCB14 include the corresponding enabling signals K1 to K14.

The MPU 30 of the control node 90 first normally assigns time slots andgenerates normal enabling signals K1 to K3. Here, for simplification,the enabling signals K1 to K3 are made identical and the respectiveassignment information is considered to indicate time slot assignmentsin the same cycle.

Based on the enabling signal K1 included in the control block CB1, thecontrolled node 100 transmits a transfer block TB11 in a time slot SL11,while the control node 90 transmits a transfer block TB12 in a time slotSL12.

Similarly, based on the enabling signal K2 included in the control blockCB2, the controlled node 100 transfers a transfer block TB21 in a timeslot SL21, while the control node 90 transmits a transfer block TB22 ina time slot SL22.

Assume that the MPU 60 of the controlled node 100 now judges that thedata amount of the input data S25 is very small and that a sufficienttime has passed since starting of the light emission by the lightemission circuit 42 (the above steps F1 and F2).

The MPU 60 refers to the enabling signal K3 of the next control blockCB3 and detects that a time slot SL 31 is the one assigned to its ownnode (the above step F3).

Then, the MPU 60 transmits a transfer block TB31 including lightemission suspension information indicating stopping of the lightemission and the light emission restarting time S in the time slot SL31(the above step F4).

The MPU 30 of the control node 90 generates normal time slot assignmentinformation and generates an enabling signal K4 indicating theassignment information again (the above steps G3 to G6, note M=1) whendetecting light emission suspension information indicating stopping oflight emission and the light emission restarting time S in the outputdata S20 of the signal conversion circuit 32 (the above step G2).

The MPU 60 of the controlled node 100 refers to the enabling signal K4in the control block CB4, detects that a time slot SL41 is the time slotassigned to its own node 100, and stops the emission of the infrared rayin the same time slot SL41 (the above steps F5 and F6).

Then, it waits until the time T (the above step F7). The time T is atime earlier than the light emission restarting time S by exactly onecycle as an example.

On the other hand, the MPU 30 of the control node 90 assigns time slotsoriginally for assignment to the same controlled node to other nodes(the control node 90 here) until the light emission restarting time Sarrives and generates enabling signals K5 to K11 (the above steps G7 andG8).

Then, when the light emission restarting time S arrives, it generatesthe enabling signal K12 indicating normal time slot assignmentinformation and transmits a control block CB12 (the above block G1).

The MPU 60 of the controlled node 100 which had been waiting until thetime T refers to the enabling signal K12 in the control block CB12,detects that a time slot SL121 is the time slot for its own node, andstarts the emission of the infrared ray in the same time slot SL121 (theabove steps F8 and F9).

Then, it transmits a transfer block TB131 from the next assigned timeslot SL131.

In this way, it is possible to reduce the power consumption byshortening the light emission time by a controlled node having a smallamount of input data while preventing interference with remote controlsand other existing infrared communication devices using a sub-carrierfrequency band of not less than 33 kHz and less than 6 MHZ.

Further, by stopping and starting the light emission in the controllednode so that the modulated signal component in the sub-carrier frequencyband of not less than 33 kHz and less than 6 MHZ becomes under themaximum allowable value, it becomes possible to suppress interferencewith remote controls and other existing infrared communication deviceusing the sub-carrier frequency band and to thereby enable use at thesame time as existing optical communication devices.

The MPU 60 of the above controlled node 100 was configured to determinethe stopping and restarting of emission of the infrared ray bymonitoring the data amount of the input data S25. This corresponds tojudgment by estimating the data amount to be input in the future fromthe data amount of the input data S25 input in the past.

Instead of judging by estimating in this way, it is possible totemporarily store the input data S25 in a buffer memory and determinethe stopping and restarting of the light emission from the data amountof the input data stored in the buffer memory.

In the above FIGS. 5 and 6, the emission of the infrared ray is stoppedand started instantaneously, however, as shown in FIG. 7, it is alsopossible to give a gradual transient property of an extent able to fitin an assigned time slot or of about one cycle and use this to changethe infrared ray from a predetermined signal intensity to zero signalintensity or from the zero signal intensity to a predetermined signalintensity.

For example, a time constant obtained from a capacitor and a resistormay be used to change the power source voltage of the light emissioncircuit from a predetermined voltage value to zero voltage or from thezero voltage to a predetermined voltage value.

By stopping and starting the light emission by a timing, pattern, ortransient property so that the modulated signal component in thesub-carrier frequency band of, for example, not more than 33 kHz andless than 6 MHZ, becomes under the maximum allowable value in this way,it becomes possible to suppress the modulated signal component in thesub-carrier frequency band generated by the stopping and starting oflight emission and thereby reduce the spurious waves and possible toshorten the period from the stopping of the light emission to thestarting of the light emission or from the starting of the lightemission to the stopping of the light emission.

Further, as shown in FIG. 8, it is possible to transmit a referencesignal in the same time slot SL121 at the time of restarting theemission of the infrared ray to make the preparations for reception(amplitude adjustment, synchronization adjustment, etc.) of the controlnode 90 for data to be transmitted from the controlled node 100 in thetime slot SL121.

In the optical communication system of the above first embodiment, anexample was explained where the emission of an infrared ray were stoppedand started in an assigned time slot.

However, it is also possible to providing a non-communication period(gap) between time slots and stop and start the infrared ray emissionduring the non-communication period rather than in the time slot.

In this case, it becomes possible to increase the number of time slotsable to be used for data transfer comparing with the case of stoppingand starting the light emission in a time slot, thus it is possible toprevent waste of the time slots.

Note that it is also possible to stop the light emission in a gap andstart the light emission in an assigned slot or stop the light emissionin an assigned time slot and start the light emission in a gap.

Further, in the optical communication system of the above firstembodiment, the controlled node 100 was configured to transmit to thecontrol node 90 light emission suspension information containing thestopping of the light emission and the light emission restarting time S,however, it is also possible to register in the control node 90 aplurality of patterns (or types) of different light emission suspensioninformation or light emission suspension periods and transmit to thecontrol node 90 selection information indicating which pattern (or type)to select.

Second Embodiment

A second embodiment of a wireless optical communication system accordingto the present invention will be explained next.

In the above first embodiment, whether or not to suspend light emissionfor a predetermined period was judged in a controlled node. In thesecond embodiment, it is judged in the control node.

FIG. 9 is a schematic block diagram of the configuration of a controlnode 290 and a controlled node 300 used in a wireless opticalcommunication system of the second embodiment of the present invention.

In FIG. 9, an example of one-to-one optical communication between onecontrol node 290 and one controlled node 300 is illustrated, however,the invention can also be applied to one-to-many optical communication.

Further, in FIG. 9, components of the same configuration as thecomponents of the control node 90 and the controlled node 100 in FIG. 1are given the same reference numerals and explanations of identicalcomponents are omitted.

A light emission control means 64A and an amount information generationmeans 64B in an MPU 64 in FIG. 9 have almost the same configuration asthe light emission control means 60A and the amount informationgeneration means 60B in the MPU 60 in FIG. 1, while an assignment means34A in an MPU 34 has almost the same configuration as the assignmentmeans 30A in the MPU 30 in FIG. 1.

The control node 290 comprises a transmission device (transmitter) 10, areception device (receiver) 20, a microprocessing unit (MPU) 34, aswitch 31, and a signal conversion circuit 32.

The MPU 34 is a controller for overall control of the control node 290and comprises an assignment means 34A and an instruction informationgeneration means 34B.

The assignment means 34A assigns time slots, generates assignmentinformation, and outputs an enabling signal indicating the assignmentinformation as a signal S7 to the signal conversion circuit 32.

The instruction information generation means 34B generates instructioninformation for suspending light emission by the light emission circuit42 of the controlled node 300 for a predetermined period and outputs theinstruction information as a signal S7 to the signal conversion circuit32.

The controlled node 300 comprises a transmission device (transmitter)40, a reception device (receiver) 50, an MPU 64, a switch 61, and asignal conversion circuit 62.

The MPU 64 is a controller for overall control of the controlled node300 and comprises a light emission control means 64A and an amountinformation generation means 64B.

The light emission control means 64A generates a light emission controlsignal S16 and outputs it to the light emission circuit 42.

The amount information generation means 64B monitors the input data S25to generate amount information of the input data S25, supplies theamount information to the light emission control means 64A, and outputsthe amount information as a signal S26 to the signal conversion circuit62.

The assignment means 34A included in the MPU 34 of the control node 290assigns time slots after N cycles (N≧1) based on the instruction signalS22 input to the terminal 92 from an outside device, for example, anupper layer, and the output data S20 and outputs an enabling signalindicating assignment information as a signal S7 to the signalconversion circuit 32.

Further, the instruction information generation means 34B generatesinstruction information including information to instruct stopping oflight emission of the light emission circuit 42 and the light emission.restarting time S based on the amount information in the output dataS20 and outputs it as a signal S7 to the signal conversion circuit 32.

The signal S7 is converted to a signal S9 of a format for infraredcommunication in the signal conversion circuit 32. The signal S9 issupplied to one switchable terminal a of the switch 31.

The switch 31 is receives a transfer block or a control block as asignal S6 from the signal conversion circuit 32 at the other switchableterminal b and switches the switchable terminals a and b based on theswitch control signal S8 from the MPU 34.

When transmitting a normal transfer block, the MPU 34 controls theswitch 31 to switch to the switchable terminal b side by the switchcontrol signal S8 so that the signal S6 of the transfer block istransferred as it is as a signal S1 to the transmission device 10.

When transmitting a control block, the MPU 34 controls the switch 31 toswitch the switchable terminals a and b by the switch control signal S8so that the signal S9 is inserted to part of the control block. Here,the switch 31 operates as a multiplexer. As a result, a transmissionsignal S1 having the configuration as shown in FIG. 20, wherein thesignal S9 is inserted to part of a signal S6 of the control block, canbe generated.

The signal S9 inserted to the control block at this time is a signalindicating assignment information of time slots after N cycles andapproval of time slots and is also a signal indicating the instructioninformation.

On the other hand, the light emission control means 64A in the MPU 64 ofthe controlled node 100 is supplied with output data S23 from the signalconversion circuit 62 and detects the control block from the controlnode 90.

The amount information generation means 64B in the MPU 64 generatesamount information of the input data S25 and supplies it to the lightemission control means 64A and further outputs the amount information asa signal S26 to the signal conversion circuit 62.

The light emission control means 64A refers the enabling signal and theinstruction information in the control block and controls the lightemission of the light emission circuit by the light emission controlsignal S16 to start and stop the infrared ray emission.

The signal S26 from the amount information generation means 64B is inputto the signal conversion circuit 62. The signal conversion circuit 62converts the signal S26 to a signal S27 of a format for infraredcommunication,and supplies the signal S27 to one switchable terminal aof the switch 61.

The switch 61 receives a transfer block as a signal S28 from the signalconversion circuit 62 at the other switchable terminal b and switchesthe terminals a and b based on the switch control signal S29 from theMPU 29.

The MPU 64 switches the switch 61 by the switch control signal S29 toinsert a signal S27 to part of the signal S28 of the transfer block. Atransmission signal S11 of the transfer block is output to thetransmission device from the switch 61.

Operation of Controlled Node 300

The operation of the controlled node 300 will be explained withreference to FIG. 10 and FIG. 11 next.

FIGS. 10 and 11 are schematic flow charts of the operation of acontrolled node 300 and the control operation of the MPU 64. Here, acontrol operation relating to stopping and starting of the infrared rayemission will be shown.

First, at step F11, it is judged whether a time slot is assigned to thecontrolled node 300 based on a transmission enabling signal in theoutput data S23. When an assigned time slot arrives, the routineproceeds to step F12.

At step F12, it is judged whether instruction information includinginformation to instruct stopping of infrared ray emission and a lightemission restarting time S is received.

When the instruction information is received, the routine proceeds tostep F15.

When the instruction information is not received, the routine proceedsto step F13.

At step F13, a transfer block including input data for transmission andamount information is generated and transmitted to the control node 290by using the assigned time slot.

Specifically, by outputting the signal S26 indicating amount informationto the signal conversion circuit 62 and converting it to a signal S27and by controlling the switch 61 to switch by the switch control signalS29, the signal S27 is inserted to part of the signal S28 of thetransfer block and a transmission signal S11 is generated and output tothe transmission device 40.

At step F15, it is judged whether a time slot is assigned to thecontrolled node 300 again. When the assigned time slot arrives, theroutine proceeds to step F16.

At step F16, a light emission control signal S16 for stopping the lightemission is output to the light emission circuit 42 to instruct thelight emission circuit 42 to stop light emission, then the routineproceeds to step F17. The light emission circuit 42 stops the lightemission in the assigned time slot.

At step F17, it is judged whether the current time is a time T. When thetime T, the routine proceeds to step F18. Here, the time T is a time alittle earlier than the light emission restarting time S in theinstruction information.

At step F18, it is judged whether a time slot is assigned to thecontrolled node 300 again. When the assigned time slot arrives, theroutine proceeds to step F19.

At step F19, a light emission starting signal S16 for starting the lightemission is output to the light emission circuit 42 to instruct thelight emission circuit 42 to start the light emission, then the routinereturns to step F11. The light emission circuit 42 starts the lightemission in the assigned time slot based on the light emission startingsignal S16.

Operation of Control Node 290

The operation of the control node 290 will be explained next withreference to FIG. 12 and FIG. 13.

FIGS. 12 and 13 are schematic flow charts of the operation of thecontrol node 290 and the control operation of the MPU 34. Here, thecontrol operation relating to the assignment of time slots is shown.Also, a case of a wireless optical communication system comprising acontrol node 290 and three controlled nodes 300A to 300C will beexplained.

First, at step G11, time slots are normally assigned, a control blockincluding an enabling signal corresponding to the assignment istransmitted to the controlled nodes 300A to 300C, then the routineproceeds to step G12. For example, the control node 290 assigns timeslots normally by equally assigning time slots to the control node 290and the controlled nodes 300A to 300C.

At step G12, output data S20 of the signal conversion circuit 32 isreferred to so as to judge whether amount information of the input dataS25 is received.

When the amount information is not received, the routine returns to stepG11.

When the amount information is received, the routine proceeds to stepG13.

At step G13, it is judged whether the data amount of the input data S25is very small. This is judged for example by comparing the data amountwith a predetermined data amount.

When it is judged to be not very small, the routine returns to step G11and time slots are normally assigned. Here, when a time slot assigned tothe control node 290 arrives, a transfer block including the input dataS21 is transmitted to the controlled nodes 300A to 300C in the assignedtime unit.

When the data amount is very small, the routine proceeds to step G14.

At step G14, it is judged whether a sufficient time has passed since thestarting of light emission by the light emission circuit 42. Forexample, this is judged by storing the previous light emissionrestarting time in an internal memory device and determining whether apredetermined time has passed since the previous light emissionrestarting time.

When a sufficient time has not passed, the routine returns to step G11.

When a sufficient time has passed, the routine proceeds to step G15.

At step G15, the time slots are normally assigned. Also, instructioninformation including information to instruct stopping of light emissionand information indicating (or designating) a light emission restartingtime S is generated for a controlled node having a very small dataamount and for which a sufficient time has passed (for example, thecontrolled node 300A), and a control block including the instructioninformation and an enabling signal is transmitted to the controllednodes 300A to 300C.

In the following steps G23 to G26, one or more time slots are assignedto the controlled node 300A.

This is because when the controlled node 300A receiving the instructioninformation stops the infrared ray emission, the time slot assigned tothat own node 300A is used.

At step G23, a variable x is cleared and reset to 0.

At step G24, time slots are normally assigned to the controlled nodes300A to 300C, and a control block including an enabling signalcorresponding to the assignment Is transmitted to the controlled nodes300A to 300C.

At step G25, the value of the variable x is incremented to add exactly 1when a time slot is assigned to the controlled node 300A at step G24,while the variable x is left as it is when a time slot is not assignedto the controlled node at step G24.

At step G26, it is judged whether the value of the variable x is apredetermined value M or more (M≧1).

When the value of the variable x is less than the predetermined value M,the routine returns to step G24 where time slots are normally assignedto the controlled nodes 300A to 300C.

When the value of the variable x is the predetermined value M or more,the routine proceeds to step G27.

At step G27, time slots are assigned to the controlled nodes 300B and300C other than the controlled node 300A or the control node 290, acontrol block including an enabling signal corresponding to theassignment is transmitted to the controlled nodes 300A to 300C, then theroutine proceeds to step G28.

At step G28, it is judged whether the current time is the light emissionrestarting time S.

When not yet the light emission restarting time S, the routine returnsto step 27, where time slots are assigned to the controlled nodes 300Band 300C other than the controlled node 300A or the control node 290.

When the light emission restarting time S, the routine returns to stepG11.

Note that at steps G23 to G26, time slots were normally assigned Mtimes, however, it is also possible to assign a plurality of time slotsto the controlled node 300A at one time.

At step G27, the time slots not assigned to the controlled node 300Awere assigned to nodes participating in the optical communication,however, by assigning them to nodes not participating in the opticalcommunication, it is possible to increase the number of controlled nodesparticipating in the optical communication and to increase the amount ofcommunication of nodes other than the control node 290 and thecontrolled node 300A.

Further, in a wireless optical communication system of the above secondembodiment, infrared ray emission may be stopped and startedinstantaneously as shown in FIGS. 5 and 6. It is also possible to give agradual transient property of an extent able to fit in an assigned timeslot or of about one cycle and use this to change the infrared ray froma predetermined signal intensity to zero signal intensity or from thezero signal intensity to a predetermined signal intensity as shown inFIG. 7.

By stopping and starting the light emission by a timing, pattern, or atransient property so that modulated signal component in the sub-carrierfrequency band of, for example, not less than 33 kHz and less than 6 MHZbecomes less than a maximum allowable value, the modulated signalcomponent in the sub-carrier frequency band generated by the stoppingand starting of the light emission is suppressed to reduce spuriouswaves and it is possible to shorten the period from the stopping of thelight emission to the starting of the light emission or the period fromthe starting of the light emission to the stopping of the lightemission.

Also, as shown In FIG. 8, it is possible to transmit a reference signalIn the same time slot SL121 at the time of restarting the emission ofthe infrared ray to make the preparations for reception (amplitudeadjustment, synchronization adjustment, etc.) of the control node 290for data to be transmitted from the controlled node 300 In the time slotSL121.

In the optical communication system of the above second embodiment, anexample was explained where the emission of an infrared ray were stoppedand started In an assigned time slot.

However, It Is also possible to providing a non-communication period(gap) between time slots and stop and start the infrared ray emissionduring the non-communication period rather than in the time slot.

In this case, it becomes possible to increase the number of time slotsable to be used for data transfer comparing with the case of stoppingand starting the light emission in a time slot, thus it is possible toprevent waste of the time slots.

Note that it is also possible to stop the light emission in a gap andstart the light emission in an assigned slot or stop the light emissionin an assigned time slot and start the light emission in a gap.

Third Embodiment

A third embodiment of a wireless optical communication system accordingto the present invention will be explained next.

In the above first and second embodiments, the optical communicationsystem was configured to suspend light emission of the light emissioncircuit of a controlled node for a predetermined period, however, in thethird embodiment, it is configured to suspend the light emission of thelight emission circuit of a control circuit for a predetermined period.

FIG. 14 is a schematic block diagram of the configuration of a controlnode 390 and a controlled node 400 used in the optical communicationsystem of the third embodiment of the present invention.

In FIG. 14, for simplification, the number of the control node 90 ismade one and the number of the controlled nodes is also made one,thereby giving an example of one-to-one optical communication, however,the invention can be applied to one-to-many optical communication aswell.

Further, in FIG. 14, components of the same configuration as thecomponents of the control node 90 and the controlled node 100 in FIG. 1are given the same reference numerals and explanations of identicalcomponents are omitted.

An amount information generation means 66B in the MPU 66 has almost thesame configuration as the amount information generation means 60B in theMPU 60 in FIG. 1, and an assignment means 36A in the MPU 36 in FIG. 14has almost the same configuration as the assignment means 30A in the MPU30 in FIG. 1.

The configuration node 390 comprises a transmission device 10, areception device 20, an MPU 36, a switch 31, and a signal conversioncircuit 32.

The MPU 36 comprises an assignment means 36A and a light emissioncontrol means 36B.

The assignment means 36A assigns time slots, generates assignmentinformation, and outputs an enabling signal indicating the assignmentinformation as a signal S7 to the signal conversion circuit 32.

The light emission control means 46B generates a light emission controlsignal S18 for suspending the light emission by the transmission device10 for a predetermined period and outputs it to a light emission controlterminal 12T of the light emission circuit 12.

Also, the light emission control means 36B generates light emissionsuspension information including information indicating the lightemission by the light emission circuit 12 and the light emissionrestarting time S and outputs the same as a signal S7 to the signalconversion circuit 32.

The controlled node 300 comprises a transmission device 40, a receptiondevice 50, an MPU 66, a switch 61, and a signal conversion circuit 62.

The MPU 66 comprises a light emission control means 66A and an amountinformation generation means 66B.

The light emission control means 66A generates a light emission controlsignal S16 for continuing the light emission by the light emissioncircuit 42 and outputs it to the light emission control terminal 42T ofthe light emission circuit 42.

The amount information generation means 66B monitors the input data S25to generate amount information of the input data S25 and outputs thesame as a signal S26 to the signal conversion circuit 62.

The assignment means 36A included in the MPU 36 of the control node 390assigns time slots after N cycles (N≧1) based on the instruction signalS22 input to the terminal 92 from an outside device, for example, anupper layer, and output data S20 and outputs a signal S7 indicating theassignment information to the signal conversion circuit 32.

Also, the light emission control means 36B generates light emissionsuspension information including information instructing stopping of thelight emission by the light emission circuit 12 and informationinstructing the light emission restarting time S and outputs the same asa signal S7 to the signal conversion circuit 32.

The signal S7 is converted to a signal S9 of a format for infraredcommunication, while the signal S9 is supplied to one switchableterminal a of the switch 31.

The switch 31 receives a transfer block or a control block as a signalS6 from the signal conversion circuit 32 at the other switchableterminal b and controls switching of the switchable terminals a and bbased on the switch control signal S8 from the MPU 36.

When transmitting a normal transfer block, the MPU 36 controls theswitching of the switch 31 to the switchable terminal b side by theswitch control signal S8 so that the signal S6 of the transfer block issent as it is as a signal S1 to the transmission device 10.

When transmitting a control block, the MPU 36 controls the switching ofthe switchable terminals a and b of the switch 31 by the switch controlsignal S8 so that a signal S9 is inserted to part of the control block.Here, the switch 31 operates as a multiplexer. As a result, atransmission signal S1 having the configuration as shown in the aboveFIG. 20 wherein the signal S9 is inserted to part of the signal S6 ofthe control block is generated.

At this time, the signal S9 inserted to the control block is a signalindicating time slot assignment information after N cycles and approvalof time slots and is a signal indicating light emission suspensioninformation.

On the other hand, the light emission control means 66A in the MPU 66 ofthe controlled node 400 is supplied with output data S23 from the signalconversion circuit 62 and detects a control block in the output dataS23.

The amount information generation means 66B in the MPU 66 generatesamount information of input data S25, supplies the same to the lightemission control means 66A, and further outputs the amount informationas a signal S26 to the signal conversion circuit 62.

The MPU 66 is supplied with a control block transferred from the controlnode 390, detects the enabling signal and the light emission suspensioninformation in the control block, and outputs predetermined data as asignal S26 to the signal conversion circuit 62 when data transmission isnecessary.

The signal conversion circuit 62 converts the signal S26 to a signal S27of a format for infrared communication and supplies the signal S27 toone switchable terminal a of the switch 61.

The switch 61 receives a transfer block from the signal conversioncircuit 62 as a signal S28 at the other switchable terminal b andswitches the switchable terminals a and b based on the switch controlsignal S29 from the MPU 66.

The MPU 66 switches the switch 61 by the switch control signal andinserts the signal S27 to part of the transfer signal S28. Atransmission signal S11 of the transfer block is output from the switch61 to the transmission device 40.

Operation of Controlled Node 400

The operation of the controlled node 400 will be explained withreference to FIG. 15 next.

FIG. 15 is a schematic flow chart of the operation of the controllednode 400 and the control operation of the MPU 66. Here, the controloperation relating to light emission suspension information from thecontrol node 390 is shown.

First, at step F31, it is judged whether a time slot is assigned to thecontrolled node 400 based on a transmission enabling signal in theoutput data S23. When the assigned time slot arrives, the routineproceeds to step F36.

When the assigned time slot does not arrive, the routine proceeds tostep F32.

At step F32, it is judged whether light emission suspension informationincluding information indicating suspension of the infrared ray emissionand information indicating a light emission restarting time S isreceived. Specifically, this is judged by whether any light emissionsuspension information is detected in the output data S23.

When the light emission suspension information is not received, theroutine returns to step F31.

When the light emission suspension information is received, the routineproceeds to step F33.

At step F33, it is judged whether the current time is earlier than thelight emission restarting time S and whether a requirement for datatransmission has occurred. The case where a requirement for a datatransmission has occurred is for example when the amount of the inputdata S25 sharply increases and exceeds a predetermined data amount.

When the current time is not earlier than the light emission restartingtime S or when the requirement for data transmission has not occurred,the routine returns to step F31.

When the current time is earlier than the light emission restarting timeS and data transmission is required, the routine proceeds to step F34.

At step F34, a transfer block including predetermined data istransmitted to the control node 90 using the assigned time slot, thenthe routine proceeds to step F35.

Specifically, by outputting the signal S26 indicating the predetermineddata to the signal conversion circuit 62 to convert it to the signal S27and by controlling the switching of the switch 61 by the switch controlsignal, the signal S27 is inserted to part of the signal S28 of thetransfer block and the transmission signal S11 is generated. When thecontrol node 390 receives the predetermined data, the light emissioncontrol means 36B of the control node 390 is made to generate the lightemission control signal S18 and the light emission circuit 12 is made tostart emitting light.

At step F35, it is judged whether a waiting time specifically for thecontrolled node 400 has passed from the predetermined data transmissionin the above step F34. Note that when a wireless optical communicationsystem has a plurality of controlled nodes, by setting the waiting timesso that cycles for transmitting predetermined data by the plurality ofcontrolled nodes become mutually different, it becomes possible totransmit the predetermined data at different times when the plurality ofcontrolled nodes are simultaneously required for data transmission.

When the specific waiting time has not passed, it is waited until thetime elapses.

When the specific waiting time has passed, the routine returns to stepF31.

Operation of Control Node 390

The operation of the control node 390 will be explained with referenceto FIG. 16 and FIG. 17 next.

FIGS. 16 and 17 are schematic flow charts of the operation of thecontrol node 390 and the control operation of the MPU 36. Here, thecontrol operation relating to time slots assignment is shown. Also, theoptical communication system will be explained for a case where thereare one control node 390 and three controlled nodes 400A to 400C.

First, at step G31, time slots are normally assigned, then the routineproceeds to step G32. For example, the control node 390 normally assignstime slots by equally assigning time slots to the control node 390 andthe controlled nodes 400A to 400C.

At step G32, it is judged whether the amount information of the inputdata S25 is received by referring to the output data from the signalconversion circuit 32.

When the amount information is not received, the routine returns to stepG31.

When the amount information is received, the routine proceeds to stepG33.

At step G33, it is judged whether the data amount of the input data S25and that of the input data S21 to the controlled nodes 400A to 400C arevery small. For example, when the data amounts of the input data S25 andinput data S21 are smaller than a predetermined data amount, it isjudged the data amount is very small, while when the data amount of theinput data S25 or input data S21 exceeds the predetermined data amount,it is judged that the data amount is not very small.

When it is judged to be not very small, the routine returns to step G31,where time slots are normally assigned. Here, when the data amount ofthe input data S21 exceeds the predetermined data amount, a transferblock including the input data S21 is transferred to the controllednodes 400A to 400C in the time slot assigned to the node 390.

When it is very small, the routine proceeds to step G34.

At step G34, it is judged whether a sufficient time has passed since thelight emission circuit 12 started light emission.

When a sufficient time has not yet passed, the routine returns to stepG31.

When the sufficient time has passed, the routine proceeds to step G35.

At step G35, light emission suspension information including informationindicating light emission suspension and information indicating thelight emission restarting time S is generated and transmitted to thecontrolled nodes 400A to 400C by using the control block.

At step G36, a light emission control signal S18 for stopping the lightemission is generated to instruct the light emission circuit 12 tosuspend light emission suspension, then the routine proceeds to stepG37. The light emission circuit 12 stops emitting the light based on thelight emission suspension signal S18.

Note that at step G36, a time slot may be assigned to the node 390 andthe light emission suspension signal S18 may be output to the lightemission circuit 12 in the assigned time slot.

At step G37, it is judged whether the current time is the light emissionrestarting time S.

When the light emission restarting time S, the routine proceeds to stepG39.

When not yet the light emission restarting time, the routine proceeds tostep G38.

At step G38, it is judged whether predetermined data is received or not.Specifically, this is judged by monitoring the output data S20 from thesignal conversion circuit 32 and determining whether the predetermineddata is detected in the output data S20.

When the predetermined data is not received, the routine returns to stepG37.

When the predetermined data is received, the routine proceeds to stepG39.

At step G39, a light emission control signal S18 for starting the lightemission is generated to instruct the light emission circuit 12 to startemitting the light, then the routine returns to step G31. The lightemission circuit 12 starts the light emission based on the lightemission starting signal S18.

In the control node 390, the MPU 66 may be configured to generate amountinformation of the input data S21 by monitoring the input data S21 orconfigured to be supplied with amount information of the input data S21as a signal S22 via a terminal 92.

The controlled node 400 was configured so that the light emissioncircuit 42 constantly emits light, however, it may also be configured sothat the light emission by the light emission circuit 42 may besuspended for a predetermined period based on the data amount of theinput data S25.

Also, in the optical communication system of the third embodiment, inthe control node 290, infrared ray emission may be stopped and startedinstantaneously as shown in FIGS. 5 and 6. It is also possible to give agradual transient property of an extent able to fit in an assigned timeslot or of about one cycle and use this to change the infrared ray froma predetermined signal intensity to zero signal intensity or from thezero signal intensity to a predetermined signal intensity as shown inFIG. 7.

By stopping and starting the light emission by a timing, pattern, ortransient property so that the modulated signal component in thesub-carrier frequency band of, for example, not more than 33 kHz andless than 6 MHZ, becomes under the maximum allowable value in this way,it becomes possible to suppress the modulated signal component in thesub-carrier frequency band generated by the stopping and starting oflight emission and thereby reduce the spurious waves and possible toshorten the period from the stopping of the light emission to thestarting of the light emission or from the starting of the lightemission to the stopping of the light emission.

Further, as shown in FIG. 8, it is possible to transmit a referencesignal in the same time slot SL121 at the time of restarting theemission of the infrared ray to make the preparations for reception(amplitude adjustment, synchronization adjustment, etc.) of the controlnode 390 for data to be transmitted from the controlled node 400 in thetime slot SL.

In the optical communication system of the above third embodiment, anexample was explained where the emission of an infrared ray were stoppedand started in an assigned time slot.

However, it is also possible to providing a non-communication period(gap) between time slots and stop and start the infrared ray emissionduring the non-communication period rather than in the time slot.

In this case, it becomes possible to increase the number of time slotsable to be used for data transfer comparing with the case of stoppingand starting the light emission in a time slot, thus it is possible toprevent waste of the time slots.

Note that it is also possible to stop the light emission in a gap andstart the light emission in an assigned slot or stop the light emissionin an assigned time slot and start the light emission in a gap.

Also, the optical communication system of the third embodiment wasconfigured so that the control node 390 transmitted light emissionsuspension information to the controlled node 400, however, it may alsoconfigured so that a plurality of patterns of different light emissionsuspension periods are registered in the controlled node 400 andselection information indicating which pattern to selected istransmitted to the controlled node 400.

Note that in the control nodes 90, 290, and 390, the signal conversioncircuits 32 may be respectively provided in the MPUs 30, 34, and 36,while in the controlled nodes 100, 300 and 400, the signal conversioncircuits 62 may be respectively provided in the MPUs 60, 64, and 66.

Also, the switches 31 and 61 may be configured by multiplexers.

Also, the quadrature modulation circuits 11 and 41 may have quadratureamplitude modulation (QAM) type modulators using changes of phases andamplitudes, while the quadrature demodulation circuits 22 and 52 mayhave QAM demodulators.

Note that the signal conversion circuits 32 and 62 may have errorcorrection circuits.

Also, the frequency band of the carrier modulated signal may be largerthan 6 MHZ and smaller than 60 MHZ or larger than 6 MHZ and smaller than50 MHZ.

Also, the maximum allowable value may be determined, when an infraredcommunication device is placed near the control node or controlled nodewhich suspends the light emission for a predetermined period, bymeasuring in advance a value of the modulated signal component in thesub-carrier frequency band used by the infrared communication device inthe modulated signal components carried by the infrared ray from thecontrol node or the controlled node which does not cause interferencewith the infrared communication device and by using the measured valueas the maximum allowable value or, when there are laws, regulations, orother conventions, by setting the maximum allowable value by theconventions.

In the optical communication system according to the above embodiments,by stopping and starting the light emission by a timing, pattern, or atransient property so that no serious spurious wave is caused as aresult of an increase of a modulated signal component in the sub-carrierfrequency band of not less than 33 kHz and less than 6 MHZ, it ispossible to prevent interference with remote controls, cordlessheadphones, and other existing infrared communication devices and toshorten the period of the light emission and thereby reduce the powerconsumption for the light emission.

Also, by the control nodes 90 and 290 assigning time slots which hadbeen planned to be assigned to controlled nodes suspending lightemission to other nodes, the amount of communication of the other nodescan be increased. Further, by assigning the time slots to thirdcontrolled nodes not participating in the optical communication, thenumber of controlled nodes participating in optical communication can beincreased.

Summarizing the effects of the invention, in the first opticalcommunication system according to the present invention, the lightemission of a transmission means of a second node can be suspended for apredetermined period in accordance with a data amount of input data fortransmission input to the second node and therefore the powerconsumption for light emission by the transmission means can be reduced.

Furthermore, the modulated signal component of a second frequency bandgenerated by stopping and starting the light emission in the modulatedsignal components carried by the modulated wave, that is, light, fromthe second node can be suppressed so as to not exceed a maximumallowable value.

Especially, when supposing the light is an infrared ray and the secondfrequency band is a sub-carrier frequency band used by other infraredcommunication devices, the modulated signal component in the sub-carrierfrequency band can be suppressed to avoid interference with the otherinfrared communication devices.

In the second optical communication system according to the presentinvention, it is possible to suspend the light emission for apredetermined period by a transmission device of a second node inaccordance with a data amount of input data for transmission input tothe second node and therefore reduce the power consumption for the lightemission by the transmission means.

Also, since instruction information for suspending the light emission ofthe second node for a predetermined period is generated in a first node,processing for transmitting to the first node the information indicatingthe suspension of the light emission by using an assigned time slot canbe made unnecessary in the second node.

Also, it is possible to suppress the modulated signal component of asecond frequency band generated by the stopping and starting of thelight emission in the modulated signal components carried by themodulated wave, that is, light, from the second node so as not to exceeda maximum allowable value.

Especially, when supposing the light is an infrared ray and the secondfrequency band is a sub-carrier frequency band used by other infraredcommunication devices, the modulated signal component in the sub-carrierfrequency band can be suppressed to prevent interference with the otherinfrared communication devices.

In the third optical communication system according to the presentinvention, it is possible to suspend a light emission by the firsttransmission means for a predetermined period based on the data amountof input data for transmission input to the first node and the dataamount of the input data for transmission input to the second node andthereby reduce the power consumption for the light emission by the firsttransmission means.

Further, it is possible to suppress the modulated signal component of asecond frequency band generated by stopping and starting of the lightemission in the modulated signal components carried by the modulatedwave, that is, light, from the first node so as not to exceed a maximumallowable value.

Especially, when supposing the light is an infrared ray and the secondfrequency band is a sub-carrier frequency band used by other infraredcommunication devices, the modulated signal component in the sub-carrierfrequency band can be suppressed to prevent interference with the otherinfrared communication devices.

In the first optical communication method according to the presentinvention, it is possible to suspend light emission by a second node fora predetermined period in accordance with a data amount of input datafor transmission and thereby reduce the power consumption for the lightemission by the second node.

Further, it is possible to suppress the modulated signal component of asecond frequency band generated by stopping and starting of the lightemission in the modulated signal components carried by the modulatedwave, that is, light, from the second node so as not to exceed a maximumallowable value.

Especially, when supposing the light is an infrared ray and the secondfrequency band is a sub-carrier frequency band used by other infraredcommunication devices, the modulated signal component in the sub-carrierfrequency band can be suppressed to prevent interference with the otherinfrared communication devices.

In the second optical communication method according to the presentinvention, it is possible to suspend the light emission by a first nodefor a predetermined period in accordance with a data amount of inputdata for transmission input to the second node and a data amount ofinput data for transmission input to the first node and thereby reducethe power consumption for the light emission by the first node.

Also, it is possible to suppress the modulated signal component of asecond frequency band generated by the stopping and starting of thelight emission in the modulated signal components carried by themodulated wave, that is, light, from the first node so as not to exceeda maximum allowable value.

Especially, when supposing the light is an infrared ray and the secondfrequency band is a sub-carrier frequency band used by other infraredcommunication devices, the modulated signal component in the sub-carrierfrequency band can be suppressed to prevent interference with the otherinfrared communication devices.

While the invention has been described with reference to specificembodiment chosen for purpose of illustration, it should be apparentthat numerous modifications could be made thereto by those skilled inthe art without departing from the basic concept and scope of theinvention.

What is claimed is:
 1. A wireless optical communication system having aplurality of nodes including a first node and a second node andperforming wireless optical communication between said first node andsaid second node, wherein said second node comprises: transmission meansfor transmitting input data for transmission to be input to said secondnode to said first node by using light amplitude-modulated by amodulated signal of a first frequency band; and light emission controlmeans for suspending light emission by the transmission means for apredetermined period of time based on a data amount of the input data,so that a modulated signal component in a second frequency band otherthan said first frequency band does not exceed a maximum allowablevalue.
 2. A wireless optical communication system as set forth in claim1, wherein said optical communication system performs time-divisionmultiplex mode optical communication and said first node comprises:assignment means for assigning time slots to said plurality of nodesincluding said first node and said second node and for generatingassignment information, transmission means for transmitting saidassignment information to at least said second node by using lightamplitude-modulated by a modulated signal of said first frequency band;and reception means for receiving light from said second node andextracting therefrom said input data for transmission from said secondnode; said second node further comprises reception means for receivinglight from said first node and extracting therefrom said assignmentinformation; and the transmission means of said second node transmitsthe input data for transmission to be input to said second node to saidfirst node by using said light in a time slot assigned to the secondnode.
 3. The wireless optical communication system as set forth in claim1, wherein said light emission control means suspends the light emissionby said transmission means for the predetermined period of time when adata amount of the input data for transmission to be input to saidsecond node is less than a predetermined data amount.
 4. The wirelessoptical communication system as set forth in claim 1, wherein said lightemission control means generates light emission suspension informationindicating a timing pattern and transient property for stopping andstarting of light emission before the transmission means of said secondnode stops the light emission; and the transmission means of said secondnode transmits said light emission suspension information to said firstnode by using said light prior to stopping of the light emission.
 5. Awireless optical communication system as set forth in claim 2, whereinsaid assignment means reduces the assigning of the time slots to saidsecond node in a suspended period of time where the transmission meansof said second node suspends light emission to be less than assignedoutside a suspended period or eliminates the assigning of time slots tosaid second node during said suspended period.
 6. The wireless opticalcommunication system as set forth in claim 5, wherein said assignmentmeans assigns time slots not assigned to said second node during saidsuspended period of time to nodes other than said second node among saidplurality of nodes.
 7. The wireless optical communication system as setforth in claim 5, wherein: said assignment means assigns time slots notassigned to said second node during said suspended period of time tothose of said plurality of nodes other than said first node and saidsecond nodes yet to participate in the optical communication.
 8. Thewireless optical communication system as set forth in claim 2, whereinthe transmission means of said second node stops the light emission in atime slot assigned to the second node.
 9. The wireless opticalcommunication system as set forth in claim 2, wherein the transmissionmeans of said second node starts the light emission in a time slotassigned to the second node.
 10. The wireless optical communicationsystem as set forth in claim 9, wherein the reception means of saidfirst node prepares for reception of data from the transmission means ofthe second node in the time slot where the transmission means of saidsecond node starts the light emission.
 11. The wireless opticalcommunication system as set forth in claim 2, wherein anon-communication period of time is provided between the time slotsassigned by said assignment means, and the transmission means of saidsecond node stops the light emission in said non-communication period.12. The wireless optical communication system as set forth in claim 2,wherein a non-communication period is provided between the time slotsassigned by said assignment means, and said second transmission meansstarts the light emission in said non-communication period.
 13. wirelessoptical communication system as set forth in claim 2, wherein thetransmission means of said first node transmits at least to said secondnode the input data for transmission to be input to the first node in atime slot assigned to the first node by using said light.
 14. Thewireless optical communication system as set forth in claim 1, whereinsaid second node further comprises reception means for receiving lightfrom said first node and for extracting from the light data from saidfirst node.
 15. The wireless optical communication system as set forthin claim 1, wherein said light is an infrared ray.
 16. wireless opticalcommunication system as set forth in claim 15, wherein said firstfrequency band is not less than 6 MHZ and less than 60 MHZ, and saidsecond frequency band is not less than 33 kHz and less than 6 MHZ.
 17. Awireless optical communication method for performing wireless opticalcommunication at least between a first node and a second node among aaplurality of nodes, including the steps of: transferring input data fortransmission to be input to said second node from the second node tosaid first node by using light amplitude-modulated by a modulated signalof a first frequency band; detecting a data amount of the input data fortransmission to be input to said second node; and suspending lightemission by said second node for a predetermined period of time based onsaid detected data amount so that a modulated signal component in asecond frequency band other than said first frequency band does notexceed a maximum allowable value.
 18. The wireless optical communicationmethod as set forth in claim 17, wherein time-division multiplex modeoptical communication is performed in the optical communication methodand further including the steps of: assigning time slots to saidplurality of nodes in said first node; generating assignment informationin said first node; transferring said assignment information from saidfirst node to at least said second node by using lightamplitude-modulated by a modulated signal of said first frequency band,and wherein the input data for transmission to be input to said secondnode is transferred to said first node in a time slot assigned to thesecond node in said step of transferring input data to the first node.19. The wireless optical communication method as set forth in claim 17,wherein in said step of suspending light emission by the second node fora predetermined time light emission is stopped and started when saiddetected data amount is less than a predetermined data amount.
 20. Thewireless optical communication method as set forth in claim 18, whereinin the step of generating assignment information in said first nodeassignment of time slots to said second node in a predetermined periodof time where said second node suspends the light emission is reducedfrom assignment outside the predetermined period of time or assignmentof time slots to said second node in the predetermined period iseliminated.
 21. The wireless optical communication method as set forthin claim 20, wherein in the step of generating assignment information insaid first node time slots not assigned to said second node in saidpredetermined period are assigned to nodes other than said second nodeamong said plurality of nodes.
 22. The wireless optical communicationmethod as set forth in claim 20, wherein the step of generatingassignment information in said first node assigns time slots notassigned to said second node in said predetermined period to those ofthe plurality of nodes other than said first node and said second nodeyet to participate in the optical communication.
 23. The wirelessoptical communication method as set forth in claim 18, wherein: the stepof suspending light emission by said second node for a predeterminedperiod of time includes the step of stopping the light emission in atime slot assigned to the second node.
 24. The wireless opticalcommunication method as set forth in claim 18, wherein the step ofsuspending light emission by said second node for a predetermined periodincludes the step of starting the light emission in a time slot assignedto the second node.
 25. The wireless optical communication method as setforth in claim 24, comprising the further step of performingpreparations for receiving data in said first node from said second nodein said time slot wherein said second node starts the light emission.26. The wireless optical communication method as set forth in claim 18,comprising the further step of providing a non-communication periodbetween the time slots assigned by said first node; and the step ofsuspending the light emission by said second node for a predeterminedperiod of time includes the step of stopping the light emission in saidnon-communication period.
 27. The wireless optical communication methodas set forth in claim 18, comprising the further step of providing anon-communication period between the time slots assigned by said firstnode; and the step of suspending the light emission by said second nodefor a predetermined period of time includes the step of starting thelight emission in said non-communication period.
 28. The wirelessoptical communication method as set forth in claim 17, wherein saidlight is an infrared ray.
 29. The wireless optical communication methodas set forth in claim 28, wherein said first frequency band is not lessthan 6 MHZ and less than 60 MHZ, and said second frequency band is notless than 33 kHz and less than 6 MHZ.
 30. A wireless opticalcommunication system having a plurality of nodes including a first nodeand a second node and performing wireless optical communication betweensaid first node and second node, wherein said first node comprises:first reception means for receiving light from said second node andextracting from the light data from said second node; instructioninformation generation means for generating instruction information tostop light emission by said second node for a predetermined period oftime based on amount information in said data extracted in said firstreception means; and first transmission means for transmitting saidinstruction information to said second node by using lightamplitude-modulated by a modulated signal of a first frequency band; andsaid second node comprises: reception means for receiving light fromsaid first node and extracting from the light said instructioninformation; amount information generation means for generating amountinformation of input data for transmission to be input to said secondnode; second transmission means for transmitting said amount informationgenerated by said amount information generation means to said first nodeby using light amplitude-modulated by a modulated signal of said firstfrequency band; and light emission control means for suspending lightemission by said second transmission means based on said instructioninformation extracted by said second reception means so that a modulatedsignal component in a second frequency band other than said firstfrequency band does not exceed a maximum allowable value.
 31. Thewireless optical communication system as set forth in claim 30, whereinsaid optical communication system performs time-division multiplex modeoptical communication and said first node further comprises anassignment means for assigning time slots to said plurality of nodes andgenerating assignment information; said first transmission meanstransmits to said second node said instruction information and saidassignment information by using said light; said second reception meansreceives light from said first node and extracts from the light saidinstruction information and said assignment information; and said secondtransmission means transmits to said first node the input data fortransmission to be input to said second node and said amount informationin a time slot assigned to said second node by using said light.
 32. Thewireless optical communication system as set forth in claim 31, whereinsaid assignment means reduces the assigning of time slots to said secondnode in a suspended period of time where the transmission means of saidsecond node suspends light emission to be less than the assignmentoutside the suspended period or eliminates assignment of time slots tosaid second node during said suspended period.
 33. The wireless opticalcommunication system as set forth in claim 32, wherein said assignmentmeans assigns time slots not assigned to said second node during saidsuspended period to nodes other than said second node among saidplurality of nodes.
 34. The wireless optical communication system as setforth in claim 32, wherein said assignment means assigns time slots notassigned to said second node during said suspended period to saidplurality of nodes other than said first node and said second node yetto participate in the optical communication.
 35. The wireless opticalcommunication system as set forth in claim 31, wherein the secondtransmission means of said second node stops the light emission in atime slot assigned to the second node.
 36. wireless opticalcommunication system as set forth in claim 31, wherein the secondtransmission means of said second node starts the light emission in atime slot assigned to the second node.
 37. wireless opticalcommunication system as set forth in claim 36, wherein the firstreception means prepares for reception of data from the secondtransmission means of the second node in the time slot where the secondtransmission means starts the light emission.
 38. The wireless opticalcommunication system as set forth in claim 31, wherein anon-communication period is provided between the time slots assigned bysaid assignment means, and the second transmission means of said secondnode stops the light emission in said non-communication period.
 39. Thewireless optical communication system as set forth in claim 31, whereina non-communication period is provided between the time slots assignedby said assignment means, and said second transmission means starts thelight emission in said non-communication period.
 40. The wirelessoptical communication system as set forth in claim 31, wherein the firsttransmission means of said first node transmits at least to said secondnode the input data for transmission to be input to the first node in atime slot assigned to the first node by using said light.
 41. Thewireless optical communication system as set forth in claim 30, whereinsaid instruction information generation means generates said instructioninformation when a data amount indicated by the amount information insaid data is less than a predetermined data amount.
 42. The wirelessoptical communication system as set forth in claim 30, wherein saidlight is an infrared ray.
 43. The wireless optical communication systemas set forth in claim 42, wherein said first frequency band is not lessthan 6 MHZ and less than 60 MHZ, and said second frequency band is notless than 33 kHz and less than 6 MHZ.
 44. A wireless opticalcommunication system having a plurality of nodes including a first nodeand a second node and performing optical communication at least betweensaid first node and said second node, wherein said first node comprises:first transmission means for transmitting to said second node firstinput data for transmission to be input to said first node by usinglight amplitude-modulated by a modulated signal of a first frequencyband; first reception means for receiving light from said second nodeand extracting from the light data from said second node; and lightemission control means for suspending light emission by said firsttransmission means based on amount information in said data extracted insaid first reception means and a data amount of the first input data fortransmission to be input to said first nodes so that a modulated signalcomponent in a second frequency band other than said first frequencyband does not exceed a maximum allowable value; and said second nodecomprises: amount information generation means for generating amountinformation of second input data for transmission to be input to saidsecond nodes and second transmission means for transmitting said amountinformation generated by said amount information generation means tosaid first node by using light amplitude-modulated by a modulated signalof said first frequency band.
 45. The wireless optical communicationsystem as set forth in claim 44, wherein said optical communicationsystem performs time-division multiplex optical communication and saidfirst node further comprises assignment means for assigning time slotsto said plurality of nodes and generating assignment information; saidfirst transmission means transmits at least to said second node saidassignment information by using said light; said second node receiveslight from said first node and extracts from the light said assignmentinformation; and said second transmission means transmits to said firstnode the second input data for transmission input to said second node ina time slot assigned to said second node by using said light.
 46. Thewireless optical communication system as set forth in claim 44, whereinwhen said second node needs to transmit said second input data fortransmission while in a suspended period where the first transmissionmeans of said first node has suspended the light emission, said secondnode sends predetermined data to said first node to make said firsttransmission means to start light emission.
 47. The wireless opticalcommunication system as set forth in claim 46, wherein said plurality ofnodes includes nodes other than said first node and second node; and thenodes other than said first node and said second node among saidplurality of nodes have mutually different cycles for transmitting saidpredetermined data.
 48. The wireless optical communication system as setforth in claim 44, wherein said light emission control means suspendsthe light emission by said first transmission means for a predeterminedperiod of time when a data amount of the first and second input data fortransmission is less than a predetermined data amount.
 49. The wirelessoptical communication system as set forth in claim 44, wherein saidlight emission control means generates light emission suspensioninformation indicating a timing pattern or a transient property forstopping and starting of light emission before the first transmissionmeans stops the light emission; and said first transmission meanstransmits said light emission suspension information to said second nodeprior to stopping of the light emission.
 50. The wireless opticalcommunication system as set forth in claim 44, wherein said light is aninfrared ray.
 51. The wireless optical communication system as set forthin claim 50, wherein said first frequency band is not less than 6 MHZand less than 60 MHZ, and said second frequency band is not less than 33kHz and less than 6 MHZ.
 52. A wireless optical communication method forperforming wireless optical communication between a first node and asecond node among a plurality of nodes, including the steps of:transferring first input data for transmission to be input to said firstnode from said first node to at least said second node by using lightamplitude-modulated by a modulated signal of a first frequency band;generating amount information of second input data for transmission tobe input to said second node in the second node; transferring saidamount information from said second node to said first node by usinglight amplitude-modulated by a modulated signal of said first frequencyband; and suspending light emission by said first node for apredetermined period of time based on said amount informationtransferred from said second node and a data amount of the first inputdata for transmission to be input to said first node, so that amodulated signal component in a second frequency band other than saidfirst frequency band does not exceed a maximum allowable value.
 53. Thewireless optical communication method as set forth in claim 52, whereintime-division multiplex mode optical communication is performed in theoptical communication method and further including the steps of:assigning time slots to said plurality of nodes in said first node,generating assignment information in said first node; and transferringsaid assignment information from said first node to said second node byusing light amplitude-modulated by a modulated signal of said firstfrequency band; and wherein the second input data for transmission andsaid amount information are transferred from said second node to saidfirst node in a time slot assigned to said second node by using saidlight in said step of transferring amount information to the first node.54. The wireless optical communication method as set forth in claim 52,further including the step of, when a need arises for transmission ofsaid second input data for transmission in said second node during saidpredetermined period where light emission by said first node issuspended, transmitting a predetermined data from said second node tosaid first node to make said first node start light emission.
 55. Thewireless optical communication method as set forth in claim 54, whereinsaid plurality of nodes includes nodes other than said first nodes andsaid second node; and the nodes other than said first node and saidsecond node among said plurality of nodes have mutually different cyclesfor transmitting said predetermined data.
 56. The wireless opticalcommunication method as set forth in claim 52, wherein in said step ofsuspending, said first node suspends the light emission for apredetermined period of time when a data amount of said first and secondinput data for transmission is less than a predetermined data amount.57. The wireless optical communication method as set forth in claim 52,further including the step of generating in said first node lightemission suspension information indicating a timing pattern or transientproperty for stopping and starting light emission before the first nodestops the light emission and transferring the timing pattern ortransient property to said second node.
 58. The wireless opticalcommunication method as set forth in claim 52, wherein said light is aninfrared ray.
 59. The wireless optical communication method as set forthin claim 58, wherein said first frequency band is not less than 6 MHZand less than 60 MHZ, and said second frequency band is not less than 33kHz and less than 6 MHZ.